Air filters comprising a filter element of fibrous material supported at its marginal edges by a stiff paper frame are well known in the prior art. Typically, such filters are generally rectangular in shape and are provided with a porous backing sheet, e.g., bottlecap scrap, supported by the filter frame adjacent to the filter element. Various cross-sectional configurations for the filter frame have been developed in the prior art. For example, Greason, U.S. Pat. No. 3,003,581, discloses a conventional air filter in which the frame is channel-shaped in cross section, while Dow, U.S. Pat. No. 2,965,197, discloses a cross-sectional configuration in the form of an isosceles triangle and Kershaw, U.S. Pat. No. 3,938,973, discloses a cross section in the shape of a right triangle. These filters are generally lightweight in construction but somewhat bulky to handle in shipment and storage.
When packaged for shipment or storage, a plurality of filters are packed in a single container, e.g., a dozen per box. Although each filter is light in weight, it occupies a relatively large amount of space in contrast to its small weight. Since shipping and storage costs are usually based on volume, there are relatively high transportation costs associated with these filters. Indeed, the shipping and storage costs represent a considerable part of the total cost of the filters to consumers. As a result, it is highly advantageous to provide an air filter construction which requires less space for shipment and storage than the conventional filters known in the art.
There have been previous attempts in the prior art to reduce the shipping and storage space required for air filters. Several proposals have involved the design of a filter frame which is collapsible to allow the air filters to be compressed into a smaller space for shipment or storage. Examples of this type of proposal are disclosed in Hickin, U.S. Pat. No. 3,429,434; Getzin, U.S. Pat. No. 3,467,257; and Champlin, U.S. Pat. No. 4,086,071. However, the collapsible air filter structure has not yet received any widespread commercial acceptance. In addition, it has been proposed to provide air filters with flared frames to permit a set of filters to be more compactly packaged in a container for shipment and storage. Examples of the flared frame construction are disclosed in Best, U.S. Pat. No. 3,023,839; Copenhefer, U.S. Pat. Nos. 3,830,045 and 3,970,440; and Latakas, U.S. Pat. No. 4,105,423. However, the flared frame designs have been somewhat less rigid in construction than the conventional filter frames.
In view of the constantly escalating costs of transportation, there is a definite need for improvements in the construction of existing air filters to allow the filters to be more compactly packaged to conserve space and minimize shipping and storage costs. Moreover, it is highly desirable to provide an air filter construction which achieves the same strength and rigidity associated with the conventional air filters already known.